During pregnancy the previously poor vasodilatory response of uterine artery endothelium (UA Endo) to agonists such as ATP is now enhanced through a greatly prolonged Capacitative Ca2+ entry (CCE), and this results in enhanced activation of eNOS. Since P-UA Endo's enhanced function now approaches that of other vessels, increases in uterine blood flow also occur. In preeclamptic (PE) subjects who often show elevated VEGF and TNF, this sustained Ca2+ response to ATP is also lost, along with a blunting of NO output. VEGF165 signals through ERK-1/2 to cause transient inhibitory phosphorylation of the Gap junction protein, Cx43 and loss of adapted CCE Ca2+ signaling. U0126 blockade can reverse this 0x43 phosphorylation and rescue pregnancy adapted Ca2+ burst function on subsequent challenge with ATP. Brief TNF mediated Src activation also directly phosphorylates CX43 on Tyr 265, causing Cx43 inhibition that is reversible by PP2. Long term.Src activation can also promote Tyr phosphorylation of ZO-1 and disassociation from Cx43, so causing Gap junction disassembly and 0x43 movement away from cell contact points and loss of pregnancy adapted CCE function. To that end: Specific Aim 1 investigates the hypothesis that in P-UAEC, HUVEC and HUAEC that VEGF165 or TNF can mediate the dose dependent inhibition of sustained Ca2+ signaling through ERK or Src mediated direct CX43 protein phosphorylation. Specific Aim 2 investigates the further hypothesis that these same VEGF or TNF mediated inhibitory effects in P-UAEC, HUVEC and HUAEC may also promote ZO-1 protein dissociation from CX43 wherever we see chronic activation of the Src pathway. Specific Aim 3 translates Aims 1 and 2 back to intact vessels (UA Endo - pregnant sheep and HUV Endo or HUA Endo - normal human cords); by testing the hypothesis that the inhibitory actions of VEGF and TNF on endothelial Ca2+ observed in Aims 1 and 2 causes corresponding inhibition of NO production in vivo. Specific Aim 4 tests the hypothesis that together even low doses of VEGF and TNF synergize to inhibit normal endothelial function in all vessels studied through the co-activation of Src and ERK-1/2 inhibitory pathways. A new therapy to treat PE may result from these studies.